Vehicle control operations, such as automobile cruise control, may depend upon environmental conditions and related forces affecting the motion of the vehicle. For example, road grade is an environmental condition that may oppose or promote the longitudinal motion of a vehicle, and, therefore, a control operation such as cruise control may adjust according to the resultant effect from a particular road grade on the vehicle. Other conditions that may affect the motion of a vehicle, alone or in combination with road grade and each other, include forces acting on the vehicle from headwinds, changes in vehicle mass, and other aerodynamic effects. It is desirable, but currently difficult, for a vehicle control system to accurately and efficiently model a total of such forces acting on the vehicle.